Waves

1. Waves

2. What is a wave? • a wave is a disturbance that travels through a medium from one location to another. • a wave is the motion of a disturbance

3. Types of Waves • Mechanical • Waves that require a medium • Examples: sound waves, water waves, waves in a rope, and shock waves • Electromagnetic • Waves that do not require a medium (can travel through empty space) • Examples: radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays

4. Longitudinal Waves • This type of wave is called a LONGITUDINAL wave. • The pulse is transferred through the medium of the slinky, but the slinky itself does not actually move. • It just displaces from its rest position and then returns to it. • So what really is being transferred?

5. Energyis being transferred. • The metal of the slinky is the MEDIUM in that transfers the energy pulse of the wave. • The medium ends up in the same place as it started … it just gets disturbed and then returns to it rest position. • The same can be seen with a stadium wave.

6. Transverse waves • A second type of wave is a transverse wave. • We said in a longitudinal wave the pulse travels in a direction parallel to the disturbance. • In a transverse wave the pulse travels perpendicular to the disturbance. • Forms a SINE wave

7. Longitudinal vs. Transverse • The differences between the two can be seen

8. Anatomy of a Wave • In our wave here the dashed line represents the equilibrium position. • Once the medium is disturbed, it moves away from this position and then returns to it

9. Anatomy of a Wave • The points A and F are called the CRESTS of the wave. • This is the point where the wave exhibits the maximum amount of positive or upwards displacement

10. Anatomy of a Wave • The points D and I are called the TROUGHS of the wave. • These are the points where the wave exhibits its maximum negative or downward displacement.

11. Anatomy of a Wave • The distance between the dashed line and point A is called the Amplitude of the wave.\ • This is the maximum displacement that the wave moves away from its equilibrium.

12. Anatomy of a Wave • The distance between two consecutive similar points (in this case two crests) is called the wavelength. • This is the length of the wave pulse. • Between what other points is can a wavelength be measured?

13. Wave frequency • We know that frequency measure how often something happens over a certain amount of time. • We can measure how many times a pulse passes a fixed point over a given amount of time, and this will give us the frequency.

14. Wave frequency • Suppose I wiggle a slinky back and forth, and count that 6 waves pass a point in 2 seconds. What would the frequency be? • 3 cycles / second • 3 Hz • we use the term Hertz (Hz) to stand for cycles per second.

15. Wave Period • The period describes the same thing as it did with a pendulum. • It is the time it takes for one cycle to complete. • It also is the reciprocal of the frequency. • T = 1 / f • f = 1 / T

16. Wave Speed • We can use what we know to determine how fast a wave is moving. • What is the formula for velocity? • velocity = distance / time • What distance do we know about a wave • wavelength • and what time do we know • period

17. Wave Speed • so if we plug these in we get • velocity = length of pulse / time for pulse to move pass a fixed point • v =  / T • we will use the symbol  to represent wavelength

18. Wave Speed • v =  / T • but what does T equal • T = 1 / f • so we can also write • v = f  • velocity = frequency * wavelength • This is known as the wave equation.